Finished lubricants used for automobiles, diesel engines, axles, transmissions, and industrial applications consist of two general components, a base oil and one or more additives. Base oil is the major constituent in these finished lubricants and contributes significantly to the properties of the finished lubricant. In general, a few base oils are used to manufacture a wide variety of finished lubricants by varying the mixtures of individual base oils and individual additives.
Although lubricating base oils traditionally have been prepared from conventional petroleum feedstocks, recent studies have shown that high quality lubricating base oils can be prepared from unconventional waxy feedstocks, such as slack waxes, deoiled slack waxes, refined foots oils, waxy lubricant raffinates, normal paraffin waxes, NAO waxes, waxes produced in chemical plant processes, deoiled petroleum derived waxes, microcrystalline waxes, Fischer-Tropsch waxes, and mixtures thereof. Since these unconventional waxy feedstocks are primarily composed of normal paraffins (n-paraffins), these feedstocks initially have poor low temperature properties, such as pour point and cloud point. In order to improve the low temperature properties of the waxy feedstocks, selective branching must be introduced into the hydrocarbon molecules, as for example, through hydroisomerization. See, for example, U.S. Pat. Nos. 5,135,638; 5,543,035; and 6,051,129.
Base oils are usually prepared from hydrocarbon feedstocks having a major portion boiling above about 340° C. (about 650° F.). Typically, the feedstocks from which lubricating base oils are prepared are recovered as part of the bottoms from an atmospheric distillation unit. This high boiling bottoms material may be further fractionated in a vacuum distillation unit to yield cuts with pre-selected boiling ranges. Most lubricating base oils are prepared from that fraction or fractions where a major portion boils above about 370° C. (about 700° F.) and below about 565° C. (about 1050° F.). In the present invention at least three side draws are collected from the vacuum tower in addition to the heaviest bottoms product and the light overhead. In addition, the vacuum tower is operated alternately in two different block modes, and the products of the side draws are blended in the appropriate proportions to product base oil products having pre-selected properties. The process of the invention offers the flexibility to produce a wide range of base oil products tailored to meet market demand. The process scheme which constitutes the present invention also saves on capital costs by requiring fewer storage tanks at the processing site.
As used in this disclosure the word “comprises” or “comprising” is intended as an open-ended transition meaning the inclusion of the named elements, but not necessarily excluding other unnamed elements. The phrase “consists essentially of” or “consisting essentially of” is intended to mean the exclusion of other elements of any essential significance to the composition. The phrase “consisting of” or “consists of” is intended as a transition meaning the exclusion of all but the recited elements with the exception of only minor traces of impurities.